docs: def _merge_mappings(*args):
      """Merges a sequence of dictionaries and/or tuples into a single dictionary.
  
      If a given argument is a tuple, it must have two elements, the first of which is a sequence of keys and the second
      of which is a single value, which will be mapped to from each of the keys in the sequence.
      """
      dct = {}
      for arg in args:
          if isinstance(arg, dict):
              merge = arg
          else:
              assert isinstance(arg, tuple)
              keys, value = arg
              merge = dict(zip(keys, [value]*len(keys)))
          dct.update(merge)
      return dct